[HUDSON-6628] change LDAPSecurityRealm to extend AbstractPasswordBasedAuthentication

so it gets the createCliAuthenticator stuff, and CLI will accept --username, etc.
In my tests this worked when passing credentials to run a command.
Login seemed to work, but commands after that were still as anonymous,
so something still missing.


git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@33773 71c3de6d-444a-0410-be80-ed276b4c234a